The present invention relates to a gyroscope suitable for remote-controlled helicopters such as aerial photographing helicopters or agricultural chemicals sprinkling helicopters.
In order to manipulate a model helicopter, the gyroscope (tail stabilizer) is an auxiliary device essential for stabilizing the yaw-axis control. Without the gyroscope mounted, the helicopter horizontally yaws because of no autonomous stability function to the yaw-axis.
In the yaw-axis control operation of a model helicopter, the yaw axis is rotated under control commands from the transmitter on the controlling gear side so that the nose of the helicopter is turned in a target direction. The gyroscope stops the rotation of the yaw-axis when control commands do not come from the controlling gear side but quickly rotates the yaw-axis in response to control commands from the controlling gear side. That is, it is necessary to perform the reciprocal control. In the gyroscope configuration for a model helicopter, the rotational speed of the helicopter is detected by computing an error between a signal from an angular velocity detection sensor equipped to a model helicopter and a reference signal being a target angular velocity value. The resultant signal is transmitted to the yaw-axis control actuator on the helicopter and is subjected to feedback control to null the angular velocity of the yaw-axis.
Conventionally, the P (proportional) control system, which can provide a simplified configuration, has been employed as the feedback control method. In the P control system, the output from the controller is proportional to an error of a measurement value to a target value.
FIG. 2 is a block diagram illustrating a conventional gyroscope employing the P control system, for model helicopters. Referring to FIG. 2, reference numerals 21, 4, 5 and 8 represent addition points; 22 represents a P controller; 3 represents a correct-pitch to yaw-axis control mixing unit; 6 represents an actuator; 7 represents a yaw-axis driving unit; 9 represents an airframe; and 10 represents a yaw-axis angular velocity detection sensor.
A rate gyroscope or piezoelectric vibration type gyroscope (iezoelectric vibration type angular velocity detection sensor), for example, is used as the yaw-axis angular velocity detection sensor 10. An error between the angular velocity signal measured by the yaw-axis angular velocity detection sensor 10 and the angular velocity zero reference value is obtained at the addition point 21 and then is input to the P controller 22. The output of the P controller 22 is added to the output signal from the correct pitch to yaw-axis control mixing unit 3 at the addition point 4. Furthermore, the addition point 5 adds the resultant signal to the yaw-axis control signal and then sends the result to the actuator 6. The yaw-axis driving unit 7 varies the pitch angle of the tail rotor in response to the output from the actuator 6, thus varying the drive force around the yaw-axis.
At the virtual addition point 8, the output from the yaw-axis driving unit 7 is added to a disturbance factor such as a counterforce of the main rotor or wind. The resultant sum is sent to the airframe 9. The yaw-axis angular velocity detection sensor 10 detects the angular velocity around the yaw-axis of the airframe 9. The detected output is coupled to the addition point 21. There is a control loop (not shown in FIG. 2) by which yaw-axis control signals are provided when the operator of a wireless controlled helicopter manipulates the stick of a wireless control device to transmit remote control signals to the airframe while observing angles around the yaw-axis of the airframe 12.
In order to perform the yaw-axis control operation in the gyroscope employing the P control system, the output signal from the yaw-axis angular velocity detection sensor 10 functions as an angular velocity correction signal. The manipulation side provides a yaw-axis control signal with an opposite polarity to that of the angular velocity correction signal. The rotary motion of the yaw-axis occurs according to the resultant difference. The yaw-axis angular velocity detection sensor 10 handles a disturbance factor as the yaw-axis control signal. A rotary motion occurs proportionally to an angular velocity offset acting as the input of the P controller 22. As a result, the conventional system has the disadvantage in that it is difficult to hover the helicopter accurately because the yaw-axis shifts due to a disturbance factor such as side wind.
Recently, the PID control system built-in gyroscope for model helicopters that can cancel the offset being the drawback of the above-mentioned P control system has been commercially introduced. The PID control system performs an integration operation for integrating existing errors and then outputting the result value and a differential operation for outputting values proportional to changes in error, in addition to the proportional operation for handling the output of an adjuster as a value proportional to the error. The differential operation is not solely used but is used to improve the proportional operation and the integration operation. For that reason, in the patent specification, the P control system and the PID control system are handled as the same meaning.
It is expected that the gyroscope employing the PID control system will be widely used in future because it can cancel its offset and can provide excellent control characteristics to a disturbance factor such as wind. In the PID control system, the yaw-axis control signal from the manipulation side offsets the reference signal on the gyroscope side. In other words, the control signal acts as an angular velocity command signal.
In order to control the ascent, the descent, the ascending rate, or the descending rate of a model helicopter in the conventional manipulating system, the correct pitch operation (for changing the elevation angle at the same time) which varies the pitch angle of each of the main rotor blades is performed. In this case, a change in pitch angle causes the counter torque to the yaw-axis of the helicopter to be changed. Hence, the operator varies the pitch angle of the tail rotor according to variations in correct pitch angle to change the operation amount of the yaw-axis. That is, the mixing process ranging from the correct pitch operation to the yaw-axis operation is automatically changed. The mixing operation means that the operation amount from the manipulation side to the correct pitch operation channel is added to the yaw-axis operation channel, with a predetermined ratio and a predetermined changing characteristic provided.
In the gyroscope employing the P control system shown in FIG. 2, the correct pitch operation control signal is input to the addition point 4 via the correct-pitch to yaw-axis control signal mixing unit 3 and then to the yaw-axis control system.
However, the PID control system built-in gyroscope has the disadvantage in that since the yaw-axis control signal is handled as an angular velocity command signal, the same mixing operation as that in the P control system cannot be performed. In the PID control system, variations in counter torque can be automatically canceled under the I-control operation, without the mixing operation. However, employing only the I-control system leads to poor control response characteristics.